Hydraulic accumulator comprising a position indicator

ABSTRACT

The invention relates to a hydraulic accumulator comprising: a) an accumulator housing ( 1 ) consisting of a non-magnetisable material and defining an axial direction of the housing; b) a separating element ( 9 ) that can be axially displaced in the accumulator housing ( 1 ) and separates two working chambers ( 5, 7 ) from each other in the accumulator housing ( 1 ); c) a field-generating magnetic configuration ( 29 ) arranged on the separating element; and d) a series of magnetic field sensors ( 35 ) which are arranged on the outer side of the accumulator housing ( 1 ), extend along the path of the axial movement of the separating element ( 9 ) and react to the field of the magnetic configuration ( 29 ) on the separating element ( 9 ), in order to characterise the position thereof along the series of magnetic field sensors ( 35 ).

The invention relates to hydraulic accumulators such as those provided,among other things in conjunction with hydraulic assemblies, to receivespecific volumes of a fluid under pressure (such as a hydraulic medium)and to return these volumes to an assembly as required. Hydropneumatic(gas-charged) accumulators are currently used in most hydraulicassemblies, the movable separating element inside the accumulatorhousing separating a fluid space as one working chamber from a gassupply space as the other working chamber. Nitrogen gas is normally usedas working gas and the gas-tight separating element, such as a piston ifa piston-type accumulator is involved, to a great extent permitsseparation of gas supply space from fluid space.

The fluid component is connected to the hydraulic circulation of theassembly, so that the accumulator receives fluid as the pressure risesand as it does the gas is compressed. As pressure drops the compressedgas expands and in the process forces the pressurized fluid stored backinto the hydraulic circulation. The changes in the volumes of gas supplyspace and fluid space result in corresponding axial movement of theseparating element inside the accumulator housing.

A prerequisite for the trouble-free operation of hydraulic accumulatorsdesired is that the gas precharging pressure prevailing in the gassupply space be of a value adapted to the pressure level of the fluidcomponent, so that the separating element, that is, the piston in thecase of piston-type accumulators, be in a suitable position inside thecylinder housing, a position such that the separating element canexecute the operating movements required in the axial direction betweenthe end positions in the accumulator housing.

In view of the foregoing the object of the invention is to develop ahydraulic accumulator which permits determination by simple means,during operation, of the extent of the volumes of the working chambersand accordingly determination of the position of the separating element.

It is claimed for the invention that this object is attained by ahydraulic accumulator having the characteristics (a) to (d) specified inclaim 1.

The hydraulic accumulator claimed for the invention accordingly makesavailable contact-free indication of the position of the separatingelement transmitted to the exterior through the wall of the accumulatorhousing, this making simple and reliable monitoring of the operationalstatus of the hydraulic accumulator during operation possible.

If the hydraulic accumulator is a piston-type accumulator in which acylindrical tube is provided as the accumulator housing, a tube in whichthe piston making up the separating element may be displaced axiallyover a piston stroke path, the row of magnetic field sensors on theexterior of the cylindrical tube is mounted more or less over the entirestroke path of the piston.

In one especially advantageous exemplary embodiment the piston is in theform of a non-magnetizable material and the configuration of magnetsgenerating the magnetic field on the piston has a plurality of permanentmagnets distributed over the circumferences of the piston; these magnetsare in alignment with each other in relation to the axial direction.

One especially simple design provides for the magnetic field sensors onthe exterior of the cylindrical tube a row of movable, preferablybar-like, permanent magnets; those magnets which are oriented toward thefield generated on the piston by the configuration of magnets may bedeflected by this field to an indicator position. The bar-like permanentmagnets then function as visually detectable indication markings thedeflection of which provides a direct optical indication of therespective piston position.

By preference the rod-like permanent magnets may be deflected against aslight resetting force, so that, if the magnetic field of the pistonmoves out of its range during displacement of the piston, the magnetsautomatically return to their initial position. Provision may be madefor this contingency such that, for example, the bar-like permanentmagnets are mounted so as to be freely pivotable for their deflectionmovement about pivot axes which are positioned outside the centers ofgravity of the bar-like permanent magnets so that the force of gravityin effect exerts a resetting moment on the bar-like permanent magnets.

Special steel or a non-ferritic metal alloy such as an aluminum alloyor, if pressure of limited level is involved, optionally a plastic, maybe provided as material for the non-magnetizable accumulator housing.

The invention will be described in detail below with reference to anexemplary embodiment illustrated in the drawing, in which

FIG. 1 presents a longitudinal section of an exemplary embodiment of thehydraulic accumulator claimed for the invention in the form of apiston-type accumulator,

FIG. 2 a longitudinal section on a scale somewhat larger than that ofFIG. 1 exclusively of the piston of the exemplary embodiment along lineIII-III in FIG. 3, and

FIG. 3 a top view of the piston shown separately in FIG. 2.

The exemplary embodiment shown in the drawing of the hydraulicaccumulator claimed for the invention is that of a piston-typeaccumulator with an accumulator housing in the form of a cylindricaltube 1 which defines a longitudinal axis 3. In the cylindrical tube 1 apiston 9 as separating element may be moved in the axial directionbetween a gas supply space 5 and a fluid space 7. By a method customaryfor piston-type accumulators the piston 9 has, in annular grooves madein its circumferential surface, piston seals 11 and piston guide means13 which permit low-friction and gas-tight guiding of the piston 9 alongthe longitudinal axis 3.

The cylindrical tube 1 is closed on the end closing the gas supply space5 by a screwed-in cylinder cover 15. A gas channel 17, to which a gasvalve or a charging fitting (both not shown) may be connected, extendsthrough the cylinder cover 15.

The cylindrical tube 1 is similarly closed on the end associated withthe fluid space 7 by a screwed-in cover 19 having a central fluidpassage 21.

The piston 9 has a depression in the form of an interior trough 23 whichis concentric with the axis 3 and is open on the end of the pistonfacing the gas supply space 5 so that the volume of the gas supply space5 is increased. An annular element 25 concentric with the axis 3 isjoined by connecting bolts 27 to the piston 9 on the side of the pistonhaving the open end of the trough 23. This annular element 25, theinterior annular opening of which is in alignment with the opening edgeof the trough 23 of the piston 9, is made of a non-magnetizablematerial, by preference the same material as that of the piston 9. Theannular element 25 functions as supporting ring for permanent magnets 29which are embedded in the circumferential surface of the annular element25 concentric with the cylindrical tube 1 so that their radiallyexterior polar end surfaces 28 (FIG. 2) are spaced a short radialdistance from the circumference of the piston 9 and accordingly from theinterior wall of the cylindrical tube 1; see FIG. 3, in which the jacketsurface of the piston 9 is designated as 31.

As is to be seen in FIG. 3, in the exemplary embodiment described herefifteen permanent magnets are mounted around the circumference of thepiston 9 at regular angular distances from each other, the permanentmagnets 29 being mounted with the same polarity orientation so that theradially exterior polar end surfaces 28 form like magnetic poles.

As is to be seen in FIG. 1, during operation the piston 9 may be movedalong a piston stroke path between an upper end position in which theannular element 25 is adjacent to the upper cylinder cover 15 and alower end position in which the opposite side of the piston 9 approachesthe lower cover 19. In movement between these end positions thepermanent magnets mounted on the annular element 25 of the piston 9 moveover the length of a sensor strip 33 extending along the exterior of thecylindrical tube 1. Mounted on the strip is a row of permanent magnetswhich in the example illustrated are in the form of small bar magnets 35(only a few of which are indicated in the figure), the row of barmagnets 35 extending more or less over the entire length of the sensorstrip 33. The bar magnets 35 are mounted pivotably in pivot bearings 37(only some of which are indicated in the figure), the pivot axesextending perpendicularly to the longitudinal axis 3 and in parallelwith the tangents on the adjacent circumference of the cylindrical tube1. With the permanent magnets 35 mounted in this manner the magneticfield generated by the permanent magnets 29 on the annular element 25 ofthe piston 9 may cause these magnets 35 to be deflected along thelongitudinal section of the sensor strip 33 on which the permanentmagnets 29 are mounted. In FIG. 1 this deflection is illustrated for thepiston position indicated, in which the piston is situated a smalldistance from the upper cylinder cover 15. As is to be seen in FIG. 1,with the piston in this position the third bar magnet 35 (counting fromthe top) is deflected to the horizontal position, while the adjacentsecond bar magnet 35 and fourth bar magnet 35 are partly deflected.

This deflection of the bar magnets 35 permits determination of therespective position of the piston 9 inside the cylindrical tube 1 byvisual comparison with the non-deflected other magnets 35 of the sensorstrip 33.

The bar magnets 35 may be provided with signal coloring in order to makethe display eye-catching.

The bar magnets 35 may be mounted on the sensor strip 33 so that thedeflection of bar magnets 35 by the magnetic field on the piston 9 isopposed by a slight resetting force, so that the bar magnets 35 servingas indicator element during excursion of the magnetic field, that is,during stroke movement of the piston 9, automatically return to aninitial or non-indicator position. The resetting force may be applied inany suitable manner, such as simply by positioning the pivot axes 37 ofthe bar magnets 35 outside their center of gravity so that the barmagnets 35 are reset automatically when the magnetic field does notexert its effect. In order to generate a resetting force for the barmagnets 35 so that they extend in parallel with the longitudinal axis 3when the deflecting magnetic field is absent, the sensor strip 33 itselfcould be configured as a device generating a weak magnetic field; forexample, the sensor strip itself could be in the form of a weak barmagnet.

As has already been stated, in the invention a non-magnetizable materialis provided for the cylindrical tube 1, the piston 9, and the annularelement 25 of the latter. For example, a non-magnetizable steel (specialsteel), a non-ferritic metal alloy, aluminum alloy, or even a plasticmaterial may be provided for the cylindrical tube 1, depending on thepressure level for which the accumulator is provided.

1. A hydraulic accumulator having (a) an accumulator housing (1) ofnon-magnetizable material which defines the axial direction of thehousing, (b) a separating element (9) which may be moved in the axialdirection in the accumulator housing (1) and which separates two workingchambers (5, 7) from each other in the accumulator housing (1), (c) amagnet configuration (29) generating a field and mounted on theseparating element (9), and (d) a row of magnetic field sensors (35)mounted on the exterior of the accumulator housing (1) and extendingalong the path of axial movement of the separating element (9), whichmagnetic field sensors (35) respond to the field of the configuration ofmagnets (29) on the separating element (9) in order to mark the positionof such field along the row of magnetic field sensors
 35. 2. Thehydraulic accumulator as claimed in claim 1, wherein a cylindrical tube(1) is provided in which the piston (9) forming the separating elementmay be displaced axially over a piston stroke path, and wherein the rowof magnetic field sensors (35) on the exterior of the cylindrical tube(1) extends more or less over the entire path of the stroke of thepiston (9).
 3. The hydraulic accumulator as claimed in claim 2, whereinthe piston (9) is in the form of a non-magnetizable material and whereinthe configuration of magnets has a plurality of permanent magnets (29)mounted so as to be distributed around the circumference of the piston(9), such permanent magnets (29) being in alignment with each other inrelation to the axial direction.
 4. The hydraulic accumulator as claimedin claim 3, wherein there is provided as magnetic field sensors on theexterior of the cylindrical tube (1) a row of movable, preferablybar-shaped, permanent magnets (35), it being possible to deflect themagnets of this row which are oriented toward the field generated by theconfiguration (29) of magnets on the piston (9) into an indicatorposition by such field.
 5. The hydraulic accumulator as claimed in claim4, wherein the bar-shaped permanent magnets (35) for their deflectionmovement are mounted so as to be pivotable about respective pivot axes(37) which are perpendicular to the axial direction of the cylindricaltube (1) and are at least approximately in parallel with the directionof the tangent on the adjacent circumferential area of the cylindricaltube (1).
 6. The hydraulic accumulator as claimed in claim 5, whereinthe pivot axes (37) of the bar-shaped permanent magnets (35) arepositioned outside the centers of gravity of such permanent magnets(35).
 7. The hydraulic accumulator as claimed in claim 3, wherein thereis mounted, as carrier for the permanent magnets (29) of theconfiguration of magnets of the piston (9), an annular element (25) of anon-magnetizable material mounted on the end side of such piston (9),which annular element (25) is of a diameter smaller than the interiordiameter of the cylindrical tube (1) and into the circumferentialsurface of which annular element (25) concentric with the cylindricaltube (1) the permanent magnets (29) are introduced so that their polaraxis extends in the radial direction.
 8. The hydraulic accumulator asclaimed in claim 7, wherein the radially exterior polar end surfaces(28), which for all permanent magnets (29) are mounted with the samepolarity orientation, are positioned a small distance from the interiorwall of the cylindrical tube (1).
 9. The hydraulic accumulator asclaimed in one of claim 1, wherein special steel, an aluminum alloy, ora plastic material is provided as material for the non-magnetizableaccumulator housing (1).